The need for packaging of food and beverage products for storage and sale has increased with the increase in human populations and as urbanization has intensified. In addition, the demand for convenient, ready-to-eat products have added to the demand for suitable packaging. A long standing technique for packaging certain foods and beverages is metal cans. Such cans take a variety of geometric shapes and are often produced out of drawn and ironed steel or aluminum. Typically, these containers are either circular, oval, or rectangular (including square) in cross-section and are used to package a wide variety of liquid beverages, fruit and vegetables, meat products, dehydrated foods, etc.
The rising demand for steel and aluminum containers, though, carries certain concerns about production costs and the quantity of material used in the fabrication process. Accordingly, there have been intensified efforts to reduce the wall diameter of steel and aluminum cans in order to reduce the weight and mass of raw material used to create a can of given volume. This saves in the costs of production in two ways. By reducing the quantity of material, lower raw material costs result. Moreover, the energy required to refine or recycle the material is reduced. Another advantage is a reduction in the need for virgin raw materials that must be extracted from the natural resource base. Indeed, due to the volume of cans, such as aluminum cans for example, even a very minor reduction in wall thickness can result in literally tens of millions of dollars in savings on an annualized base. This is additionally true if there can be a reduction in thickness of an aluminum lid that is typically seamed onto an aluminum can body since the seamed lid is substantially thicker than the can body.
Nonetheless, the reduction in wall thickness of containers is not without its problems. While a reduced wall thickness is highly desirable from a material standpoint, structural integrity of the container must be maintained. Since the reduced wall thickness of a container diminishes its inherent strength, improved geometries have been developed to give added strength of the design. An example of such a geometry in the beverage industry, is the formation of a concaved depression in the bottom of an aluminum can with this concaved depression being commonly referred to as a “dome”.
Providing the bottom of a container with an axial, internally extending dome has several advantages. The margin of the dome provides a U-shaped profile that increases the structural rigidity of the container, especially where the internal contents of the container are pressurized. The provision of a dome on such a container has allowed manufacturers to maintain adequate side wall and end wall strengths while reducing the thickness of the can blank material.
This is of particular importance to the beverage industry where carbonated beverages are packaged in the container for storage and sale. Here, the dome structure greatly increases the resistance of the container to expansion or “bloating” so as to maintain integrity of the container while at the same time maintaining the contents of the container at the desired pressurized state. The lids that are seamed upon such can bodies also have a U-shaped margin that provides structural rigidity to the can.
In the typical production of a beverage can, a can blank is produced by stamping a cup-shaped blank out of sheet material. This cup-shaped blank has a bottom wall and side wall thickness that is greater than the thickness of the can to be produced, but the physical dimensions of the cup-shaped can blank are smaller than the can to be produced. The production blank is placed in an ironing device wherein a punch advances the can blank through drawing and ironing dies which configure the can blank into the final dimensions of the desired container. This is accomplished by stretching or “ironing” the metal side walls of the can blank to increase its axial dimension while thinning the wall thickness to compensate for the increase in height. This device is commonly referred to as a “body maker”. After the can body is created, a dome is configured in the integrally formed body end closure by a “domer”. The domer can be associated with the body maker or can be a separate device. Where associated with the body maker, the bottom dome structure is formed at the end of the draw and iron cycle. Alternatively, the can body may be placed in a separate doming machine. In either case, a punch strikes the bottom end closure against a die structure that is configured to match the dome shape of the punch thereby to stamp the bottom profile in the container.
Even though significant advances have occurred in the formation of container structures, there needs to be continued advancement in this art in an effort to achieve the accommodates noted above. There is a continuing need for end closures, can bodies, containers and methods which allow the further reduction in material consumption without otherwise significantly compromising the integrity of the container system. The present invention is directed to these issues.